1. Field
Embodiments described herein relate generally to methods of fabricating a semiconductor device.
2. Description of Related Art
Rapid thermal annealing (RTA) using a halogen lamp is a conventionally employed annealing method. Forming a shallow impurity diffused layer is difficult by using RTA, however. This is because impurity ions (e.g., boron (B) ions, phosphorus (P) ions, arsenic (As) ions, or the like) implanted into a semiconductor substrate diffuse in RTA because these ions have large diffusion coefficients in the semiconductor substrate (e.g., silicon (Si) substrate). It is possible to carry out the annealing at a lower temperature in order to restrain the diffusion of the impurity ions. The lowering of the annealing temperature, however, involves a problem of making the impurities less active, and thus increasing the electrical resistance of the impurity diffused layer. For this reason, with the conventional RTA processing using a halogen lamp, it is difficult to form a low-resistant, shallow impurity diffused layer (having a depth of 20 nm or less).
Under the circumstances, techniques that enable the formation of a low-resistance, shallow impurity diffused layer have been studied in recent years. One of the studied techniques is an annealing method using a flash lamp filled with a noble gas, such as xenon (Xe) (hereafter, the method will be referred to as the flash lamp annealing). Another one of the studied techniques is an annealing method using a CO2 laser or the like (hereafter, the method will be referred to as the laser annealing). Both the flash lamp annealing and the laser annealing are ultra-short time annealing methods on a millisecond order (hereafter, referred to as the millisecond annealing (MSA)). Since being the ultra-short time and high-temperature annealing methods, the flash lamp annealing and the laser annealing achieve both the restraining of the diffusion of impurity ions and a higher activation of the impurity ions, and thereby enable the formation of a low-resistance, shallow impurity diffused layer (see, for example, Patent Document 1). In MSA, a semiconductor substrate has to be preliminarily heated before the annealing since the semiconductor substrate is annealed to a high temperature within a short period of time. Specifically, a preliminarily-heating process with a halogen lamp precedes the flash lamp annealing (see, for example, Patent Document 1). In this way, the MSA makes it possible to form a low-resistance, shallow impurity diffused layer. However, due to the annealing of such an ultra-short period of time, the MSA possibly fails to sufficiently fix up the crystal defects formed in the semiconductor substrate at the ion implantation. The crystal defects that are not fixed up sufficiently may cause electric current to flow through the crystal defects, i.e., the junction leakage. The junction leakage may cause various problems, such as an increase in the electric power consumption and failure of the ON/OFF action of the transistor.
To address these problems, Patent Document 2 discloses a method using the flash lamp annealing and Spike RTA (spike rapid thermal annealing) in combination. The flash lamp annealing can activate the impurity ions whereas the Spike RTA can fix up the crystal defects formed in the semiconductor substrate. Fixing up the crystal defects by the Spike RTA, however, requires heating the semiconductor substrate to a relatively high temperature (e.g., 1000° C. or higher). Such a high temperature diffuses the impurity ions implanted in the semiconductor substrate, thereby making it difficult to form a shallow impurity diffused layer.